1. Field of the Invention
The present invention relates to a process for preparing a hydrophilic polymer film, and particularly, to a process for the preparation of a hydrophilic polymer film which comprises modifying the polymer film, by coating a photopolymerization solution containing a hydrophilic monomer of low water swelling ability and a UV stabilizer, on the polymer film surface that has been pre-treated with high frequency radiation, and photopolymerizing the solution thereon so as to improve the hydrophilic property, climate-resistibility, and blocking property of the polymer film.
2. Description of the Prior Art
Generally, polyolefin films have been widely used in the fields of agriculture and packaging because of their good mechanical properties, optical property, nontoxic property, and durable flexibility. However, since the surface of such conventional films are hydrophobic, the transparency of such conventional films is significantly reduced by condensation of moisture on the inner surface thereof, when used in a simple green house built by such polymer films, and the transmittance of sunlight through such films is reduced.
As a result, the yield of crops of vegetables in a simple green house is reduced and the period of harvest takes a longer time. Also, the temperature effect in the green house is reduced. If drops of water that are condensed on the surface of such films flow down onto the flower of a crop cultivated in the green house, the crop withers or fails to bear fruit.
Due to the hydrophobic property of the film surface, a coating material, such as water soluble ink, gelatin and so on, is difficult to coat onto the surface thereof. When such films are used for packaging foods, the foods may become spoiled or decayed due to the drops of water that form on the package film surface.
In order to avoid the above problems, the film surface has been modified as follows.
For example, there is a method for preparing a hydrophilic film by compounding polyethylene resin and a special surfactant, and a method for modifying the polyethylene film by coating a special surfactant on the surface thereof. However, since the surfactant used on the film is easily washed away by drops of water, the hydrophilic property of such films is reduced.
Recently, there has been developed a method for modifying such films by grafting a hydrophilic material on polyethylene film. The film modified by this method continuously maintains the hydrophilic property. However, discoloration of the film may occur since climate-resistibility is poor, and a blocking phenomena (sticking between the film) occurs on the film surface when a hydrophilic substance having a high water swelling ability, such as acrylic acid, methacrylic acid, acrylamide, methacrylamide, 2-hydroxyethylmethacrylate, and N-vinylpyrrolidone, is used.